The spinning of poly(p-phenylene terephthalamide) into high strength fibers is taught in U.S. Pat. No. 3,767,756. The polymer may be prepared for example by the technique described in U.S. Pat. No. 3,850,888. The procedure described in said patent suggests the use of substantially stoichiometric amounts of reactants.
Normally, in order to obtain the highest molecular weight polymer under given conditions, stoichiometric amounts of the monomers are used in the polymerization and the polymer should contain about equal amounts of amine and acid end groups or their derivatives.